A terrorist attack on the U.S. power grid could be more destructive than superstorm Sandy, possibly costing hundreds of billions of dollars and leading to thousands of deaths, the National Academy of Sciences said.

While such an event probably wouldn’t kill people immediately, it could cause widespread blackouts for weeks or months, according to a recently declassified report released today [Wednesday] by the Academy. If it occurred during extreme weather, heat stress or exposure to cold may lead to “hundreds or even thousands of deaths,” the authors of the study wrote.

“An event of this magnitude and duration could lead to turmoil, widespread public fear, and an image of helplessness that would play directly into the hands of the terrorists,” they said.